The present invention is a method and apparatus for the direct production from molten metal of scale-free, finished gage, metal strip by continuous casting of a hot thin strip. Surface oxide removal is with a reducing gas while the cast hot thin metal strip is at an elevated temperature from retained heat of the molten metal.
Production of flat rolled steel strip, by current state-of-the-art processes, is carried out by continuously casting refined steel into a thin slab, followed by hot rolling of the slab to reach a thickness which can be put into coil form for subsequent processing. In that process, the surface of the coiled, hot rolled steel is heavily oxidized from processing steps carried out at an elevated temperature while being exposed to the atmosphere. Such oxides (scale) typically consist of Fe2O3, Fe3O4 and FeO. A next step in the production of the flat rolled steel strip typically involves removing the oxides by processing the strip in an acid pickling solution prior to rolling the strip to finished gage in a cold rolling mill.
Current methods of processing flat rolled steel strip require use of hot and cold rolling mill equipment requiring significant capital expenditures, large amounts of energy for operating, and a large plant facility for its installation. In addition, use of acid pickling solutions for removing surface oxides and disposal of spent acid solution, present environmental concerns which are resulting in more stringent regulations and increased costs for disposal.
In an effort to reduce or eliminate hot and cold rolling steps, methods are being developed to continuously cast thin strip which approaches finished gage thickness. Oxides are still present on the surface however and problems associated with oxide removal with use of acid pickling solutions continue to exist.
It is the object of the present invention to provide a process for producing finished gage thin steel strip free of surface oxides, without the use of acid pickling solutions, and without the use of extensive hot and cold rolling equipment.
The present invention is a method and apparatus for the direct production of scale-free thin metal strip from molten metal by continuously casting molten metal into a hot thin metal strip and, while the cast strip still retains heat from the molten metal, passing it through a chamber containing a reducing gas to remove oxides from the surface of the strip so as to produce a metal strip free of surface oxides. The hot strip is then cooled to a temperature below about 150xc2x0 C. prior to exposing the strip surface to any oxidizing atmosphere. In other embodiments of the invention, hot rolling of the hot thin metal strip and/or cold rolling of the cooled thin metal strip is carried out to reduce the strip thickness and modify mechanical properties of the metal. In still other embodiments of the invention the surface of the cooled thin metal strip is brushed, re-textured or coated with a protective or decorative coating.